Chapter 2 - Atoms, Molecules, and Ions PDF

Chapter 2 Atoms, Molecules, and Ions Section 2.1 The Early History of Chemistry Early History of Chemistry  Greeks were the first to attempt to explain why chemical changes occur.  Alchemy dominated for 2000 years.  Several elements discovered.  Mineral...

Chapter 2 Atoms, Molecules, and Ions Section 2.1 The Early History of Chemistry Early History of Chemistry  Greeks were the first to attempt to explain why chemical changes occur.  Alchemy dominated for 2000 years.  Several elements discovered.  Mineral acids prepared.  Robert Boyle was the first “chemist”.  Performed quantitative experiments.  Developed first experimental definition of an element. Copyright © Cengage Learning. All rights reserved 2 Section 2.2 Fundamental Chemical Laws Three Important Laws  Law of conservation of mass (Lavoisier):  Mass is neither created nor destroyed in a chemical reaction.  Law of definite proportion (Proust):  A given compound always contains exactly the same proportion of elements by mass. Copyright © Cengage Learning. All rights 3 reserved Section 2.2 Fundamental Chemical Laws Three Important Laws (continued)  Law of multiple proportions (Dalton):  When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers. Copyright © Cengage Learning. All rights 4 reserved Section 2.3 Dalton’s Atomic Theory Dalton’s Atomic Theory (1808)  Each element is made up of tiny particles called atoms. Copyright © Cengage Learning. All rights reserved 5 Section 2.3 Dalton’s Atomic Theory Dalton’s Atomic Theory (continued)  The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways. Copyright © Cengage Learning. All rights reserved 6 Section 2.3 Dalton’s Atomic Theory Dalton’s Atomic Theory (continued)  Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative numbers and types of atoms. Copyright © Cengage Learning. All rights reserved 7 Section 2.3 Dalton’s Atomic Theory Dalton’s Atomic Theory (continued)  Chemical reactions involve reorganization of the atoms—changes in the way they are bound together.  The atoms themselves are not changed in a chemical reaction. Copyright © Cengage Learning. All rights reserved 8 Section 2.4 Early Experiments to Characterize the Atom J. J. Thomson (1898—1903)  Postulated the existence of negatively charged particles, that we now call electrons, using cathode-ray tubes.  Determined the charge-to-mass ratio of an electron.  The atom must also contain positive particles that balance exactly the negative charge carried by electrons. Copyright © Cengage Learning. All rights reserved 9 Section 2.4 Early Experiments to Characterize the Atom Cathode-Ray Tube Copyright © Cengage Learning. All rights reserved 10 Section 2.4 Early Experiments to Characterize the Atom Ernest Rutherford (1911)  Explained the nuclear atom.  The atom has a dense center of positive charge called the nucleus.  Electrons travel around the nucleus at a large distance relative to the nucleus. Copyright © Cengage Learning. All rights reserved 11 Section 2.5 The Modern View of Atomic Structure: An Introduction  The atom contains:  Electrons – found outside the nucleus; negatively charged.  Protons – found in the nucleus; positive charge equal in magnitude to the electron’s negative charge.  Neutrons – found in the nucleus; no charge; virtually same mass as a proton. Copyright © Cengage Learning. All rights reserved 12 Section 2.5 The Modern View of Atomic Structure: An Introduction  The nucleus is:  Small compared with the overall size of the atom.  Extremely dense; accounts for almost all of the atom’s mass. Copyright © Cengage Learning. All rights reserved 13 Section 2.5 The Modern View of Atomic Structure: An Introduction Nuclear Atom Viewed in Cross Section Copyright © Cengage Learning. All rights reserved Section 2.5 The Modern View of Atomic Structure: An Introduction Isotopes  Atoms with the same number of protons but different numbers of neutrons.  Show almost identical chemical properties; chemistry of atom is due to its electrons.  In nature most elements contain mixtures of isotopes. Copyright © Cengage Learning. All rights reserved 15 Section 2.5 The Modern View of Atomic Structure: An Introduction Two Isotopes of Sodium Copyright © Cengage Learning. All rights reserved Section 2.5 The Modern View of Atomic Structure: An Introduction  Isotopes are identified by:  Atomic Number (Z) – number of protons  Mass Number (A) – number of protons plus number of neutrons Copyright © Cengage Learning. All rights reserved 17 Section 2.5 The Modern View of Atomic Structure: An Introduction EXERCISE! A certain isotope X contains 23 protons and 28 neutrons.  What is the mass number of this isotope?  Identify the element. Mass Number = 51 Vanadium Copyright © Cengage Learning. All rights reserved 18 Section 2.6 Molecules and Ions Chemical Bonds  Covalent Bonds  Bonds form between atoms by sharing electrons.  Resulting collection of atoms is called a molecule. Copyright © Cengage Learning. All rights reserved 19 Section 2.6 Molecules and Ions Chemical Bonds  Ionic Bonds  Bonds form due to force of attraction between oppositely charged ions.  Ion – atom or group of atoms that has a net positive or negative charge.  Cation – positive ion; lost electron(s).  Anion – negative ion; gained electron(s). Copyright © Cengage Learning. All rights reserved 20 Section 2.6 Molecules and Ions EXERCISE! A certain isotope X+ contains 54 electrons and 78 neutrons.  What is the mass number of this isotope? 133 Copyright © Cengage Learning. All rights reserved 21 Section 2.6 Molecules and Ions CONCEPT CHECK! Which of the following statements regarding Dalton’s atomic theory are still believed to be true? I. Elements are made of tiny particles called atoms. II. All atoms of a given element are identical. III. A given compound always has the same relative numbers and types of atoms. IV. Atoms are indestructible. Copyright © Cengage Learning. All rights reserved 22 Section 2.7 An Introduction to the Periodic Table The Periodic Table  Metals vs. Nonmetals  Groups or Families – elements in the same vertical columns; have similar chemical properties  Periods – horizontal rows of elements Copyright © Cengage Learning. All rights reserved 23 Section 2.7 An Introduction to the Periodic Table The Periodic Table Section 2.7 An Introduction to the Periodic Table Groups or Families  Table of common charges formed when creating ionic compounds. Group or Family Charge Alkali Metals (1A) 1+ Alkaline Earth Metals (2A) 2+ Halogens (7A) 1– Noble Gases (8A) 0 Copyright © Cengage Learning. All rights reserved 25 Section 2.8 Naming Simple Compounds Naming Compounds  Binary Compounds  Composed of two elements  Ionic and covalent compounds included  Binary Ionic Compounds  Metal—nonmetal  Binary Covalent Compounds  Nonmetal—nonmetal Copyright © Cengage Learning. All rights reserved 26 Section 2.8 Naming Simple Compounds Binary Ionic Compounds (Type I) 1. The cation is always named first and the anion second. 2. A monatomic cation takes its name from the name of the parent element. 3. A monatomic anion is named by taking the root of the element name and adding –ide. Copyright © Cengage Learning. All rights reserved 27 Section 2.8 Naming Simple Compounds Binary Ionic Compounds (Type I)  Examples: KCl Potassium chloride MgBr2 Magnesium bromide CaO Calcium oxide Copyright © Cengage Learning. All rights reserved 28 Section 2.8 Naming Simple Compounds Binary Ionic Compounds (Type II)  Metals in these compounds form more than one type of positive ion.  Charge on the metal ion must be specified.  Roman numeral indicates the charge of the metal cation.  Transition metal cations usually require a Roman numeral.  Elements that form only one cation do not need to be identified by a roman numeral. Copyright © Cengage Learning. All rights reserved 29 Section 2.8 Naming Simple Compounds Binary Ionic Compounds (Type II)  Examples: CuBr Copper(I) bromide FeS Iron(II) sulfide PbO2 Lead(IV) oxide Copyright © Cengage Learning. All rights reserved 30 Section 2.8 Naming Simple Compounds Polyatomic Ions  Must be memorized (see Table 2.5 on pg. 65 in text).  Examples of compounds containing polyatomic ions: NaOH Sodium hydroxide Mg(NO3)2 Magnesium nitrate (NH4)2SO4 Ammonium sulfate Copyright © Cengage Learning. All rights reserved 31 Section 2.8 Naming Simple Compounds Formation of Ionic Compounds To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright © Cengage Learning. All rights reserved 32 Section 2.8 Naming Simple Compounds Binary Covalent Compounds (Type III)  Formed between two nonmetals. 1. The first element in the formula is named first, using the full element name. 2. The second element is named as if it were an anion. 3. Prefixes are used to denote the numbers of atoms present. 4. The prefix mono- is never used for naming the first element. Copyright © Cengage Learning. All rights reserved 33 Section 2.8 Naming Simple Compounds Prefixes Used to Indicate Number in Chemical Names Copyright © Cengage Learning. All rights reserved 34 Section 2.8 Naming Simple Compounds Binary Covalent Compounds (Type III)  Examples: CO2 Carbon dioxide SF6 Sulfur hexafluoride N2O4 Dinitrogen tetroxide Copyright © Cengage Learning. All rights reserved 35 Section 2.8 Naming Simple Compounds Flowchart for Naming Binary Compounds Copyright © Cengage Learning. All rights reserved 36 Section 2.8 Naming Simple Compounds Overall Strategy for Naming Chemical Compounds Copyright © Cengage Learning. All rights reserved 37 Section 2.8 Naming Simple Compounds Acids  Acids can be recognized by the hydrogen that appears first in the formula—HCl.  Molecule with one or more H+ ions attached to an anion. Copyright © Cengage Learning. All rights reserved 38 Section 2.8 Naming Simple Compounds Acids  If the anion does not contain oxygen, the acid is named with the prefix hydro– and the suffix –ic.  Examples: HCl Hydrochloric acid HCN Hydrocyanic acid H2S Hydrosulfuric acid Copyright © Cengage Learning. All rights reserved 39 Section 2.8 Naming Simple Compounds Acids  If the anion does contain oxygen:  The suffix –ic is added to the root name if the anion name ends in –ate.  Examples: HNO3 Nitric acid H2SO4 Sulfuric acid HC2H3O2 Acetic acid Copyright © Cengage Learning. All rights reserved 40 Section 2.8 Naming Simple Compounds Acids  If the anion does contain oxygen:  The suffix –ous is added to the root name if the anion name ends in –ite.  Examples: HNO2 Nitrous acid H2SO3 Sulfurous acid HClO2 Chlorous acid Copyright © Cengage Learning. All rights reserved 41 Section 2.8 Naming Simple Compounds Flowchart for Naming Acids Copyright © Cengage Learning. All rights reserved Section 2.8 Naming Simple Compounds EXERCISE! Which of the following compounds is named incorrectly? a) KNO3 potassium nitrate b) TiO2 titanium(II) oxide c) Sn(OH)4 tin(IV) hydroxide d) PBr5 phosphorus pentabromide e) CaCrO4 calcium chromate Copyright © Cengage Learning. All rights reserved 43